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Author Topic: CB750F3 Rear Master cylinder Problem  (Read 935 times)

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Offline pmurph1x

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CB750F3 Rear Master cylinder Problem
« on: February 05, 2013, 12:04:16 AM »
The rear master cylinder and other components were pretty much caked in solid brake fluid crystals on my '78 CB750F. I got most of it cleaned up but I've been battling one "hole" for the last Hour. I'm starting to think that there really isnt a hole there.

If you look at the first picture you can see that there appears to be 2 holes - I would expect 1 to be a supply and the other a return just like the front brake master cylinder.


I got the large hole cleaned up no problem but ive been at the other hole with a high E guitar string and brake cleaner and still cant poke my way through the schmutz thats in there. If I look into the cylinder bore I dont see any evidence of that hole going all the way through.
Does anyone know if there really is a through hole there?

Here is a pic of the cylinder bore



Thanks
       Paul
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Offline madmtnmotors

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Re: CB750F3 Rear Master cylinder Problem
« Reply #1 on: February 05, 2013, 04:02:32 AM »
Yep, there's definitely a return hole there. Just finished refurb of the brakes on my F3 750.
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Offline Tugboat

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Re: CB750F3 Rear Master cylinder Problem
« Reply #2 on: February 05, 2013, 10:41:10 AM »
Keep digging! Just went through this with the rear mc on my buddy's GL1100.. same deal. You could only see one hole but after a while digging around in there, finally found the other one. Good luck!
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Offline pmurph1x

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Re: CB750F3 Rear Master cylinder Problem
« Reply #3 on: February 05, 2013, 12:59:14 PM »
Thanks guys. I'll keep digging. I left it soaking in simple green today so maybe it'll be a bit softer when I go at it later.
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Offline Thousandson

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Re: CB750F3 Rear Master cylinder Problem
« Reply #4 on: February 05, 2013, 06:26:32 PM »
I'm going to be cleaning out mine soon to. Ick, i was hoping not to deal with this problem. Maybe a really small drill bit then so more poking? (Thats what she said) I think it'll work.
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Offline BeSeeingYou

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Re: CB750F3 Rear Master cylinder Problem
« Reply #5 on: February 05, 2013, 07:39:37 PM »
My F1 has a similar enough MC and that return hole is very hard if at all to see looking up into the bore.  Very tiny.  It is kind of like a funnel from view in the top photo.
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Offline pmurph1x

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Re: CB750F3 Rear Master cylinder Problem
« Reply #6 on: February 05, 2013, 11:26:45 PM »
Well the Simple green didnt do much. I tried a narrow sewing needle and that didnt do much either.

In the end I chucked about 2 inches of the high E guitar string in the drill so that 1 inch was sticking out of the chuck. It worked well. It was cleared in a few seconds. Wish I had done this sooner.
Thanks for the inputs everyone.
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